1. Field of the Invention
This invention relates to buoyant alarm devices which float in a body of water and provide an indication of a disturbance to a quiescent water level. The invention relates more particularly to an improved circuit arrangment for use with such an alarm device.
2. Description of the Prior Art
A form of alarm device is known which is adapted to float in a body of water and to provide an indication of a disturbance to a quiescent level of the body of water. Such a device is particularly useful with unattended swimming pools to signal an accidental fall into the pool by a person, or, the unauthorized use of the pool. One such device includes first and second electrodes, the first of which is supported above the quiescent water level and contacts the water when the device heels as a result of water waves accompanying a disturbance to the body of water. The second electrode is normally maintained in contact with the body of water. When the device heels and the first electrode contacts the water, a circuit is closed which initiates an alarm indication.
At times it is desirable to provide an indication of the disturbance at a station which is remote to the body of water. Such an occasion arises, for example, in conjunction with the monitoring of an unattended home swimming pool when it is desirable to provide an alarm signal inside the home rather than only in the pool area. Prior arrangments have utilized a transmitting means which is supported by the buoyant device for broadcasting a radio frequency alarm signal to the remote station. These prior arrangments have energized the transmitter and broadcast a continuous radio frequency signal upon the occurence of the disturbance, and, they have alternatively energized the transmitter and broadcast an alarm signal for only a very brief interval of time, e.g. 50 ms. In the latter case, the brief signal is intended to set a latch circuit at the receiver which causes sounding of an audible alarm. However, continous broadcasting tends to rapidly deplete batteries used with the device thus necessitating frequent checking and replacement. Broadcasting a very brief signal operates to preserve battery energy but the short signal is particularly susceptible to signal loss as a result of interfering electrical noise and atmospheric conditions which can block reception of the short communication. Both of the prior arrangments are also susceptible to false alarms because of electrical noise and interfering services. Moreover, the prior arrangments have been relatively complex and costly to fabricate. It is desirable to provide a transmitter arrangment for use with a buoyant alarm device which is substantially free from the effects of interfering electrical noise and other services, which broadcasts a radio frequency signal for a period of time sufficient to assure reception and recognition at the remote location, which does not rapidly deplete battery power sources and which can be fabricated economically.